Fuel injector with premix pilot nozzle

ABSTRACT

An apparatus for injecting premixed fuel and air through a center body and into the combustion zone of a gas turbine includes a fuel injector nozzle with a premix pilot nozzle having a plurality of premix passages in fluid communication with an air supply and a fuel supply that premixes air and fuel within the premix passages. The apparatus has either an active or passive fuel feed control. Fuel can be fed to the apparatus either conventionally or as a breech load circuit integrated into the oil cartridge. Fuel can be supplied passively via a fuel channel connecting the swozzle fuel plenum to the premix passages. Alternatively, fuel can be injected from the oil cartridge into the premix passages.

DIVISIONAL APPLICATION

The present application is a divisional application of U.S. applicationSer. No. 14/102,846, filed on Dec. 11, 2013, which is incorporatedherein by reference in its entirety and for all purposes. Any disclaimerthat may have occurred during prosecution of the above-referencedapplication is hereby expressly rescinded.

FIELD OF THE INVENTION

The present invention generally involves a gas turbine engine thatcombusts a hydrocarbon fuel mixed with air to generate a hightemperature gas stream that drives turbine blades to rotate a shaftattached to the blades and more particularly to the engine's fuelinjector having a pilot nozzle that premixes fuel and air whileachieving lower nitrogen oxides.

BACKGROUND OF THE INVENTION

Gas turbine engines are widely used to generate power for numerousapplications. A conventional gas turbine engine includes a compressor, acombustor, and a turbine. In a typical gas turbine engine, thecompressor provides compressed air to the combustor. The air enteringthe combustor is mixed with fuel and combusted. Hot gases of combustionare exhausted from the combustor and flow into the blades of the turbineso as to rotate the shaft of the turbine connected to the blades. Someof that mechanical energy of the rotating shaft drives the compressorand/or other mechanical systems.

As government regulations disfavor the release of nitrogen oxides intothe atmosphere, their production as byproducts of the operation of gasturbine engines is sought to be maintained below permissible levels.Fuel-air mixing affects both the levels of nitrogen oxides generated inthe hot gases of combustion of a gas turbine engine and the engine'sperformance. A gas turbine engine may employ one or more fuel nozzles tointake air and fuel to facilitate fuel-air mixing in the engine'scombustor. The fuel nozzles may be located in a head end portion of thegas turbine engine, and may be configured to intake an air flow to bemixed with a fuel input. Typically, each fuel nozzle may be internallysupported by a center body located inside of the fuel nozzle.

Various parameters describing the combustion process in the gas turbineengine correlate with the generation of nitrogen oxides (NOx). Forexample, higher gas temperatures in the combustion reaction zone areresponsible for generating higher amounts of nitrogen oxides. One way oflowering these temperatures is by premixing the fuel air mixture andreducing the ratio of fuel to air that is combusted. As the ratio offuel to air that is combusted is lowered, so too the amount of nitrogenoxides is lowered. However, there is a trade-off in performance of thegas turbine engine. For as the ratio of fuel to air that is combusted islowered, there is an increased tendency of the pilot flame of theinjector to burn out and thus render unstable the operation of the gasturbine engine. So-called Lean Blow Out (LBO) events, which arecharacterized by extinguished flames due to an air/fuel mixture that istoo lean (insufficient fuel), increase emissions and reduce combustorefficiency.

U.S. Pat. No. 6,446,439, which is incorporated in its entirety herein bythis reference for all purposes, injects fuel into an annular passagewithin the center body where mixing with air occurs, and the premixedmixture of air and fuel is then swirled and injected as a swirlingpilot. However, combustion stability at very low levels of NOxemissions, i.e., below 3 parts per million (ppm), cannot be achieved inthis manner.

Thus, a need exists for combustion stability at very low levels of NOxemissions, i.e., below 3 parts per million (ppm). In order to achievevery low levels of NOx emissions with some margin of error andnon-uniformity around the turbine, stable operation (i.e., greatlyimproved avoidance of LBO) of the fuel injector is required.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention are set forth below in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

As used herein, a fuel supply circuit that feeds fuel only to oneinjection component, either the swozzle or the premix pilot, but notboth of them, is considered to constitute an active fuel supply. A fuelcircuit that feeds fuel to the swozzle and then feeds fuel to thepremixed pilot is considered to supply fuel actively to the swozzle andpassively to the premix pilot. An air circuit that is activelycontrolled/adjusted by means of a valve or other device external to thecombustion hardware is considered to constitute an active air supply.Air flow that is controlled by fixed orifices or passages internal tothe combustion hardware is considered a passive air supply.

One embodiment of the fuel injector with premix pilot nozzle of thepresent invention includes an apparatus for injecting premixed fuel andair from a plurality of premix passages formed in a premix pilot nozzleat the downstream end of a center body of the injector and into thecombustion zone of a gas turbine. The premix pilot nozzle may besupplied with forced air from an active air supply or with passive airsupplied through curtain air holes in a conventional swozzle disposedupstream from the premix pilot nozzle. The premix pilot nozzle may besupplied with passive air supplied downstream from a conventionalswozzle and through the fuel injector's peripheral wall from thecompressed air supplied to the head end volume of the fuel injector. Thepremix pilot nozzle may be supplied with fuel either actively orpassively. Passive fuel feed can be supplied by adding a fuel channelbetween the conventional swozzle fuel plenum through the premix pilotnozzle wall and injecting this fuel into the premix passages of thepremix pilot nozzle. The premix pilot nozzle may have fuel fedconventionally or as part of a breech load circuit integrated into theoil cartridge.

In another embodiment of the present invention, fuel could be injectedfrom the oil cartridge into the pilot premixing tubes.

Those of ordinary skill in the art will better appreciate the featuresand aspects of such embodiments, and others, upon review of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a block diagram of a turbine system having fuel nozzlescoupled to a combustor in accordance with an embodiment of the presenttechnique;

FIG. 2 is a cross-sectional view of several portions of a gas turbinesystem of the present disclosure;

FIG. 3 is a schematic representation of a cross-sectional view of a fuelnozzle with premix pilot nozzle in accordance with an embodiment of thepresent invention;

FIG. 4 is a schematic representation of a cross-sectional view takenalong the lines 4-4 in FIG. 5 of a part of a premix pilot nozzle inaccordance with an embodiment of the present invention shown in FIG. 3;

FIG. 5 is a schematic representation of a cross-sectional view takenalong the lines 5-5 in FIG. 4 of a premix pilot nozzle in accordancewith an embodiment of the present invention shown in FIG. 3;

FIG. 6 is a schematic representation of a fuel nozzle with premix pilotnozzle in accordance with another embodiment of the present invention;

FIG. 7 is a schematic representation of a cross-sectional view takenalong the lines 7-7 in FIG. 6 of a premix pilot nozzle in accordancewith an embodiment of the present invention or along the lines 7-7 inFIG. 8 of a premix pilot nozzle in accordance with another embodiment ofthe present invention;

FIG. 8 is a schematic representation of a cross-sectional view takenalong the lines 8-8 in FIG. 7 of a premix pilot nozzle in accordancewith another embodiment of the present invention;

FIG. 9 is a schematic representation of a cross-sectional view takenalong the lines 9-9 in FIG. 10 of a premix pilot nozzle in accordancewith an embodiment of the present invention;

FIG. 10 is a schematic representation of a cross-sectional view takenalong the lines 10-10 in FIG. 9 of a premix pilot nozzle in accordancewith an embodiment of the present invention;

FIG. 11 is a schematic representation of a cross-sectional view of apart of a fuel nozzle with premix pilot nozzle in accordance with afurther embodiment of the present invention;

FIG. 12 is a schematic representation of a cross-sectional view of partof a fuel nozzle with premix pilot nozzle in accordance with yet anotherembodiment of the present invention and taken along the sight linesdesignated 12-12 in FIG. 10;

FIG. 13 is a schematic representation of a cross-sectional view of partof a fuel nozzle with premix pilot nozzle in accordance with stillanother embodiment of the present invention;

FIG. 14 is a schematic cross section view of a representation of part ofa fuel nozzle with a breech-loaded premix pilot nozzle in accordancewith an additional embodiment of the present invention; and

FIG. 15 is a schematic cross section view of a representation of part ofa fuel nozzle with a breech-loaded premix pilot nozzle in accordancewith a further embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention.

Each example is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that modifications and variations can be made in thepresent invention without departing from the scope or spirit thereof.For instance, features illustrated or described as part of oneembodiment may be used on another embodiment to yield a still furtherembodiment. Thus, it is intended that the present invention covers suchmodifications and variations as come within the scope of the appendedclaims and their equivalents.

It is to be understood that the ranges and limits mentioned hereininclude all ranges located within the prescribed limits (i.e.,sub-ranges and sub-limits). For instance, a range from 100 to 200 alsoincludes sub-ranges from 110 to 150, 170 to 190, 153 to 162, and 145.3to 149.6. Further, a limit of up to 7 also includes a sub-limit of up to5, up to 3, and up to 4.5, as well as sub-ranges within the limit, suchas sub-ranges from about 1 to 5 and from 3.2 to 6.5.

Referring to FIG. 1, a simplified drawing of several portions of a gasturbine system 10 is schematically illustrated. The turbine system 10may use liquid or gas fuel, such as natural gas and/or a hydrogen richsynthetic gas, to run the turbine system 10. As depicted, a plurality offuel nozzle assemblies 12 intakes a fuel supply 14, mixes the fuel withair, and distributes the air-fuel mixture into a combustor 16. As shownin FIG. 2 for example, fuel nozzle assemblies 12 are connected to an endplate 27 of the combustor 16 by nozzle flanges 25 and fuel may besupplied passively or actively to each fuel nozzle assembly 12 throughthe end plate 27 of the combustor 16. As explained more fully below, thefuel supply 14 takes on a number of different alternative embodiments.As schematically shown in FIG. 2 for example, fuel nozzle assemblies 12may include a breech-loaded premix pilot nozzle 60 (FIG. 15) connectedto an end plate 27 of the combustor 16 by pilot flanges 29. Asschematically shown in FIGS. 2 and 6 for example, the air-fuel mixturecombusts in a combustion chamber reaction zone 32 within the combustor16, thereby creating hot pressurized exhaust gases. As schematicallyshown in FIG. 1, the combustor 16 directs the exhaust gases through aturbine 18 toward an exhaust outlet 20. As the exhaust gases passthrough the turbine 18, the gases force one or more turbine blades torotate a shaft 22 about an axis of the system 10. The shaft 22 may beconnected to various components of the turbine system 10, including acompressor 24 that also includes blades that may be coupled to the shaft22. As the shaft 22 of the turbine 18 rotates, the blades within thecompressor 24 also rotate, thereby compressing air from an air intake 23and forcing the compressed air into the combustor's head end volume 13and/or fuel nozzles 12. The shaft 22 also may be connected to amechanical load 28, which may be a vehicle or a stationary load, such asan electrical generator in a power plant or a propeller on an aircraft,for example. The load 28 may include any suitable device capable ofbeing powered by the rotational output of the turbine system 10.

FIG. 2 illustrates a cross sectional side view of portions of anembodiment of the turbine system 10 schematically depicted in FIG. 1.The embodiment of the turbine system 10 illustrated in FIG. 2 includes apair of fuel nozzles 12 located inside the head end volume 13 of acombustor 16. Each illustrated fuel nozzle 12 may include multiple fuelnozzles integrated together in a group and/or a standalone fuel nozzle,wherein each illustrated fuel nozzle 12 relies at least substantially orentirely on internal structural support (e.g., load bearing fluidpassages). In operation, air enters the turbine system 10 through theair intake and may be pressurized in the compressor 24. As schematicallyshown in FIG. 2 for example, the compressed air enters the head endvolume 13 of the combustor 16 from the diffuser exit 26. The compressedair then may be mixed with fuel (e.g., hydrocarbon gas or liquid) forcombustion within the combustor 16. For example, the fuel nozzles 12 mayinject a fuel-air mixture into the combustor 16 in a suitable ratio foroptimal combustion, emissions, fuel consumption, and power output.

As schematically shown in FIGS. 3 and 6 for example, embodiments of thenozzle assembly 12 can be formed with an axially elongating peripheralwall 38 having an air inlet 40 and a nozzle outlet 42. A center body 44extends into the nozzle assembly 12 along the longitudinal central axisof the nozzle assembly 12. As schematically shown in FIG. 6 for example,the center body 44 can include an inner cylindrical wall 54 that definesa hollow interior 51 of the center body 44. The inner cylindrical wall54 is concentrically arranged about the center or longitudinal axis ofthe nozzle assembly 12 and is configured and disposed for supplying airto the downstream end of the center body 44.

The arrows designated 30 in the FIGs., including for example FIGS. 3 and6, schematically indicate the flow of air in the direction in which thearrow is pointing. Similarly, the arrows designated 31 in the FIG.,including for example in FIGS. 4 and 6, schematically indicate the flowof fuel in the direction in which the arrow is pointing.

As schematically shown in FIG. 6 for example, the center body 44desirably can define a fuel supply passage configured as an annular fuelpassage 46 that supplies some portion of fuel to a swozzle, whichdefines a radially oriented fuel premix injection ring 48 that surroundsthe center body 44 and extends radially between the center body 44 andthe peripheral wall 38. The portion of the fuel that is supplied to theradially oriented fuel premix injection ring 48 is considered to be anactive fuel supply because it is actively controlled as it is pumpedinto the fuel premix injection ring 48. As schematically shown in FIGS.3 and 6, during operation, pressurized air exiting the compressor 24(not shown in FIGS. 3 and 6) flows into the radially outer air passage50 defined between the peripheral wall 38 and the outer wall 44 thatdefines the center body 44 of each fuel nozzle assembly 12.

The fuel premix injection ring 48 desirably includes swirler vanes 47that swirl the air flowing past the vanes 47 in the radially outer airpassage 50. Fuel outlet openings 49 (not shown in FIG. 3) are definedthrough the swirler vanes 47 of the fuel premix injection ring 48. Asschematically shown in FIG. 6, fuel from the annular fuel passage 46flows through radial fuel passages 52 into the fuel premix injectionring 48 and exits out of the fuel outlet openings 49 (not shown in FIG.3) defined through the swirler vanes 47 of the fuel premix injectionring 48. The fuel ejected from the fuel outlet openings 49 is suppliedinto the radially outer air passage 50 for premixing fuel and air in theradially outer air passage 50 upstream of the combustion chamberreaction zone 32. As air is directed against the air swirler vanes 47, aswirling pattern is imparted to the air, and this swirling patternfacilitates the mixing of the air with the primary fuel that is ejectedfrom the fuel outlet openings 49 of the air swirler vanes 47 into thepassing air flow. The air/fuel mixture exiting the radially outer airpassage 50 flows into the combustion chamber reaction zone 32, where theair/fuel mixture is combusted.

As schematically shown in FIGS. 3, 4 and 5, an exemplary embodiment ofthe premix pilot nozzle 60 defines a plurality of axially elongated,hollow premix passages 61. As schematically shown in FIGS. 3 and 4 forexample, the premix pilot nozzle 60 has an inlet 67 at the upstream endthat is connected to the downstream end of the center body 44. Thepremix pilot nozzle 60 has an outlet 68 at the downstream end that isdisposed axially opposite the upstream end of the premix pilot nozzle60. As schematically shown in FIG. 4 for example, the premix pilotnozzle 60 defines an axially extending inner channel 53 that fluidlycommunicates with the hollow interior 51 of the center body 44.

As schematically shown in FIG. 4 for example, each premix passage 61 hasan upstream end disposed near the downstream end of the center body 44.The upstream end of each premix passage 61 defines a fill opening 61 athat admits fluid to flow into the hollow premix passage 61 andcommunicates fluidly with the interior passage 51 of the center body 44.Each premix passage 61 has a downstream end disposed axially oppositethe upstream end of the premix passage 61 and that is disposed near thedownstream end of the premix pilot nozzle 60. Each downstream end ofeach premix passage 61 defines an exit opening 61 b that allows fluid todischarge from the hollow premix passage 61.

In the embodiment of the premix pilot nozzle 60 schematically shown inFIGS. 3, 4 and 5, the premix passages 61 in the premix pilot nozzle 60are defined as the hollow interiors of a plurality of premix tubes 64disposed circumferentially around the axial centerline 33 (FIG. 4) ofthe premix pilot nozzle 60. As schematically shown in FIG. 4 forexample, each premix tube 64 in this embodiment of the premix pilotnozzle 60 extends axially between an upstream end plate 65 a and adownstream end plate 65 b of the premix pilot nozzle 60. Asschematically shown in FIG. 5, there are seventeen premix passages 61arranged in a circle near the outer perimeter of the premix pilot nozzle60, which desirably has a diameter measuring about 5.1 cm. Each premixpassage 61 desirably has an axial length in the range of 7.6 cm to 12.7cm, and the diameter of each premix passage 61 desirably measures lessthan 6.35 mm and desirably has a range of 2.54 mm to 5.1 mm. Thisembodiment of the premix pilot nozzle 60 desirably attains about a threepercent air/fuel mix. However, the diameters and the number of premixpassages 61 formed in the premix pilot nozzle 60 will depend on theflows deemed optimal under the anticipated operating conditions anddesirably are determined so as to maximize mixing while maintaining thedesired fuel and air side pressure drops.

In the exemplary embodiment shown in FIGS. 3, 4 and 5, the fuel supplypassage is formed in part by a separate, fuel pipe 45 (not shown in theview of FIG. 5) that is disposed within the center body 44 and thatprovides an actively controlled supply of fuel to the plurality ofpremix passages 61 of the premix pilot nozzle 60. Thus, as far as thesupply of fuel to the premix pilot nozzle 60 is concerned, theembodiment depicted in FIGS. 3, 4 and 5 can be deemed an embodiment thatemploys an active fuel supply.

As schematically shown in FIG. 3 for example, the fuel pipe 45internally defines a fuel passage that has an upstream end disposed atthe upstream end of the center body 44 and that is configured forconnection to an actively controlled source of fuel. As schematicallyshown in FIG. 3, the actively controlled fuel is supplied to theupstream of end fuel pipe 45 through the end plate 27. As schematicallyshown in FIGS. 3 and 4 for example, the portion of the fuel supplypassage defined within the fuel pipe 45 has a downstream end that isdisposed at the downstream end of the center body 44 and that fluidlyconnects to the upstream ends of the plurality of premix passages 61. Asschematically shown in FIG. 4 for example, the downstream end of thefuel pipe 45 is connected in fluid communication with a fuel plenum 63(not discernible in the view of FIG. 3) that is defined in an embodimentof the premix pilot nozzle 60. The fuel plenum 63 is a hollow fuelpassage that forms part of the fuel supply passage and that isconfigured to extend circumferentially around the upstream end of thepremix pilot nozzle 60 and in fluid communication with the upstream endsof each premix passage 61 at a location just immediately downstream ofthe fill openings 61 a in the upstream ends of the premix passages 61.Thus, the fuel pipe 45 reaches the premix pilot nozzle 60 at thedownstream end of the center body 44 and supplies fuel to the premixpilot nozzle 60.

As schematically shown in FIG. 3, the fuel premix injection ring 48 (akaswozzle) is provided with a plurality of auxiliary air passages 43through which air 30 from the head end volume 13 (FIG. 2) passivelyenters the hollow interior 51 of the center body 44, and this passivelysupplied air flow 30 travels downstream to the premix pilot nozzle 60 atthe downstream end of the center body 44. As schematically shown in FIG.4, the air 30 travelling downstream in the hollow interior 51 of thecenter body 44 enters each fill opening 61 a of each premix passagedefined by each premix tube 64 and mixes with the fuel injected intoeach premix passage 61 and undergoes continued mixing of the fuel-airmix while the fuel-air mix travels downstream within the premix passages61. Moreover, as schematically shown in FIG. 4 for example, the fuelplenum 63 desirably communicates with each premix passage 61 near theinlet 67 of the premix pilot nozzle 60 so that the air entering therespective premix passage 61 encounters the fuel and mixes with the fuelover most of the axial length of the respective passage 61 before thefuel/air mixture leaves the respective passage 61 via its exit opening61 b. Thus, as far as the supply of air and fuel to the premix pilotnozzle 60 is concerned, the embodiment depicted in FIGS. 3 and 4 can bedeemed an embodiment that employs a passive air supply and an activefuel supply.

In the exemplary embodiment shown in FIG. 6, the elements in common withthe embodiment shown in FIGS. 3-5 are enumerated with the samedesignating numerals as found in FIGS. 3-5. However, as far as thesupply of air and fuel to the premix pilot nozzle 60 is concerned, theembodiment depicted in FIG. 6 can be deemed an embodiment that employsan active air supply and a passive fuel supply and is in this sensedifferent than the embodiment found in FIGS. 3 and 4.

As schematically shown in cross sectional views of FIGS. 6 and 7, anexemplary embodiment of the premix pilot nozzle 60 has an upstream endconnected to the downstream end of the center body 44. The premix pilotnozzle 60 defines an axially extending inner channel 53 that fluidlycommunicates with the hollow interior 51 of the center body 44. Thepremix pilot nozzle 60 has a downstream end disposed axially oppositethe upstream end of the premix pilot nozzle 60. As schematically shownin cross section in FIGS. 6 and 7, the premix pilot nozzle 60 defines aplurality of axially elongated, hollow premix passages 61, whichdesirably are arranged symmetrically and circumferentially around theaxially extending inner channel 53. Each premix passage 61 has anupstream end disposed near the downstream end of the center body 44 anddefining a fill opening 61 a that admits fluid to flow into the hollowpremix passage 61 and communicates fluidly with the interior passage 51of the center body 44. As schematically shown in FIG. 6, an activelycontrolled flow of air 30 is introduced into the interior passage 51 ofthe center body 44 and flows downstream to the fill openings 61 a of thehollow premix passages 61 of the premix pilot nozzle 60. Each premixpassage 61 has a downstream end disposed axially opposite the upstreamend of the premix passage 61 and that is disposed near the downstreamend of the premix pilot nozzle 60. Each downstream end of each premixpassage 61 defines an exit opening 61 b that allows fluid to dischargefrom the hollow premix passage 61.

Fuel is supplied from the end plate 27 (FIG. 2) into the annular fuelpassage 46. As schematically shown in FIG. 6, the radial fuel passages52 provide fuel from the annular fuel passage 46 into the fuel premixinjection ring 48. Some of the actively controlled fuel from the annularfuel passage 46 is diverted from the fuel outlet openings 49 in theswirler vanes 47 and continues flowing downstream in the annular fuelpassage 46 to provide a passive supply of fuel to the premix pilotnozzle 60 at the downstream end of the center body 44. As schematicallyshown in cross section in FIG. 6, an exemplary embodiment of the premixpilot nozzle 60 defines a fuel inlet 62 that forms part of the fuelsupply passage that fluidly connects each premix passage 61 with asource of fuel. In the embodiment of FIG. 6, the fuel inlet 62 extendsradially inwardly from the downstream end of the annular fuel passage 46so as to inject fuel into each premix passage 61 immediately downstreamof the fill opening 61 a of that premix passage 61. The activelycontrolled flow of air 30 travelling downstream in the hollow interior51 of the center body 44 enters the premix passages 61 via the fillopenings 61 a and mixes with the passive supply of fuel that is providedto the premix passages 61 of the premix pilot nozzle 60. In this manner,the air flow entering the fill opening 61 a of each premix passage 61 inthe premix pilot nozzle 60 entrains and mixes with the fuel injectedinto each premix passage 61 and undergoes continued mixing of thefuel-air mix while the fuel-air mix travels downstream within the premixpassages 61.

FIG. 8 schematically illustrates another exemplary embodiment of thepremix pilot nozzle 60 in a cross sectional view similar to the viewshown in FIG. 6, but taken along the lines 8-8 in FIG. 7. In FIG. 8, theelements in common with the embodiment shown in FIGS. 6 and 7 areenumerated with the same designating numerals as found in FIGS. 6 and 7.However, unlike the embodiment depicted in FIGS. 6 and 7, in the FIG. 8embodiment there are so-called angled premix passages 61. Asschematically shown in FIG. 8 for example, each premix passage 61 has apremix axis 34 (FIG. 12) about which its defining walls areconcentrically defined. As schematically shown in FIG. 8 for example,this centrally symmetric premix axis 34 desirably is disposed at anacute angle with respect to the symmetrically central axis 33 of thecenter body 44 and the premix pilot nozzle 60. This angle of each angledpremix passage 61 imparts to the fuel-air mix that is discharged fromthe exit opening 61 b of each premix passage 61 a radially inwardlydirected component in a direction that crosses the axial path of the airthat exits from within the axially extending inner channel 53 of thepremix pilot nozzle 60 after having passed through the hollow interior51 of the center body 44. Each angled premix passage 61 also impartsswirl to the flow of air leaving the axially extending inner channel 53of the premix pilot nozzle 60.

The magnitude of the acute angle desirably measures on the order of 4.5degrees and can range from 3 degrees to 6 degrees. Moreover, due to theacute angle, the length of the mixing path within each premix passage 61of the embodiment of the premix pilot nozzle 60 depicted in FIG. 8desirably is lengthened relative to the length of the mixing path withineach premix passage 61 in the embodiment of FIGS. 6 and 7, assuming thelengths of the premix pilot nozzles 60 are the same. Desirably, theaxial length of the premix pilot nozzle 60 measures in the range of 7.6cm to 12.7 cm and desirably has a diameter on the order of 5 cm or lessthan half the axial length of the premix pilot nozzle 60. The diametersof the premix passages 61 desirably are in the range of 2 mm to 7 mm.However, the diameters and the number of premix passages 61 formed inthe premix pilot nozzle 60 will depend on the desired flows deemedoptimal under the anticipated operating conditions and desirably aredetermined so as to maximize mixing while maintaining the desired fuelside pressure drop.

FIGS. 9 and 10 schematically illustrate another exemplary embodiment ofthe premix pilot nozzle 60 in a cross sectional view similar to the viewshown in FIG. 6, but FIG. 9 is taken along the lines 9-9 in FIG. 10, andFIG. 10 is taken along the lines 10-10 in FIG. 9. In FIGS. 9 and 10, theelements in common with the embodiments shown in FIGS. 6-8 areenumerated with the same designating numerals as found in FIGS. 6-8.However, unlike the embodiment depicted in FIGS. 6-8, in the embodimentdepicted in FIGS. 9 and 10, more than one circular grouping of premixpassages 61 is provided. An inner grouping of premix passages 61 isdisposed radially inwardly of an outer grouping of premix passages 61.As schematically shown in FIG. 10 for example, this embodiment of thepremix pilot nozzle 60 desirably includes thirty premix passages 61 andattains about a two and one half percent air/fuel mix.

In the embodiments of the premix pilot nozzle 60 schematically shown inFIGS. 6-10 for example, the premix pilot nozzle desirably is formed of asolid cylindrical metal stock in which each of the premix passages 61 isdefined by a bore through the metal stock. The number and orientation ofthe premix passages 61 are set to maximize air/fuel mixing whilemaintaining the desired fuel side pressure drop.

FIG. 11 schematically illustrates another exemplary embodiment of thepremix pilot nozzle 60 in a cross sectional view similar to the viewshown in FIGS. 8 and 9. In FIG. 11, the elements in common with theembodiments shown in FIGS. 6-10 are enumerated with the same designatingnumerals as found in FIGS. 6-10. However, internally of the center body44, the embodiment of FIG. 11 includes a cylindrical fuel cartridge 36defining a central fuel passage 37 through which an actively controlledsupply of fuel flows in the downstream direction as schematicallyindicated by the numeral 31. As further schematically indicated by thearrows designated 31 in FIG. 11 and similar to the configuration of FIG.6, a passive supply of fuel is the fuel that is diverted from the activesupply of fuel that flows from the combustor's end plate 27 (not shownin FIG. 11, see FIG. 2) and into the annular fuel passage 46 beforebeing injected into the fuel premix injection ring 48 (not shown in FIG.11). As schematically shown in FIG. 11, it is this diverted passivesupply of fuel 31 that is injected into the hollow interior 51 of thecenter body 44 via the fuel inlets 62.

As further schematically indicated by the arrows designated 30 in FIG.11, air 30 is actively supplied and flows downstream through the hollowinterior 51 of the center body 44 and carries fuel exiting from theprimary fuel inlets 62 downstream through the fill openings 61 a andinto the premix passages 61 in the premix pilot nozzle 60. In thismanner, the air flow traveling past the primary fuel inlets 62 entrainsand mixes with the fuel injected into the hollow interior 51 of thecenter body 44 and enters the fill opening 61 a of each premix passage61 in the premix pilot nozzle 60. The fuel-air mix undergoes continuedmixing while traveling downstream within the premix passages 61.

Additionally, the embodiment of FIG. 11 further defines secondary fuelinlets 62 a through the inner cylindrical wall 54 at locationsdownstream from the primary fuel inlets 62. The secondary fuel inlets 62a inject fuel directly into the premix passages 61 so that the fuel-airmix becomes enriched with fuel and undergoes additional mixing whiletraveling downstream within the premix passages 61. As schematicallydepicted in FIG. 11, both the primary fuel inlets 62 and the secondaryfuel inlets 62 a desirably are biased at an angle toward the downstreamdirection. While FIG. 11 illustrates an embodiment of the premix pilotnozzle 60 having both the primary fuel inlets 62 and the secondary fuelinlets 62 a, it is contemplated that only one set, primary 62 orsecondary 62 a, can be provided in a given alternative embodiment of thepremix pilot nozzle 60.

FIGS. 10 and 12 schematically illustrate another exemplary embodiment ofthe premix pilot nozzle 60 in a cross sectional view similar to the viewshown in FIG. 8, but FIG. 12 is taken along the lines 12-12 in FIG. 10.In FIGS. 10 and 12, the elements in common with the embodiments shown inFIGS. 6-8 are enumerated with the same designating numerals as found inFIGS. 6-8. In the embodiment schematically shown in FIGS. 10 and 12, thepremix pilot nozzle 60 is integrally formed as part of the innercylindrical wall 54 defining the hollow interior 51 of center body 44and the exterior wall 44 that defines center body. Thus, asschematically shown in FIG. 12, the inner cylindrical wall 54 definesthe radially inner walls of the premix passages 61 while the exteriorwall 44 that defines center body forms the radially outer walls of thepremix passages 61.

In embodiment schematically shown in FIGS. 10 and 12, some of premixpassages 61 have defining walls that are concentrically defined about acentral premix axis 34 (FIG. 12) that desirably is disposed parallel tothe symmetrically central axis 33 of the center body 44 and the premixpilot nozzle 60. However, unlike the embodiment depicted in FIGS. 6-8,in the embodiment depicted in FIGS. 10 and 12, more than one circulargrouping of premix passages 61 is provided, and thus there is an innercircular grouping of premix passages 61 disposed radially inwardly of anouter circular grouping of premix passages 61. Moreover, in theembodiment depicted in FIGS. 10 and 12, some of the premix passages 61have defining walls that are concentrically defined about a premix axis34 that desirably is disposed at an acute angle with respect to thesymmetrically central axis 33 of the center body 44 and the premix pilotnozzle 60.

The embodiment depicted in FIGS. 10 and 12 is similar to the exemplaryembodiment shown in FIGS. 3, 4 and 5 in that the fuel supply passage isformed in part by a separate, fuel pipe 45 that is disposed within thecenter body 44 and permits active control of the supply of fuel to thepremix passages 61. As schematically shown by the heavy typeface line inFIG. 12 for example, the fuel pipe 45 internally defines a fuel passagethat has an upstream end disposed at the upstream end of the center body44 and that is configured for connection to an actively controlledsource of fuel. As schematically shown in FIG. 12 by the arrowsdesignated by the numeral 30, air is supplied passively to the fillopenings 61 a of the premix passages 61 from the curtain air passages 57from the head end volume 13. As schematically shown in FIG. 12, theportion of the fuel supply passage defined within the fuel pipe 45 has adownstream end that is disposed at the downstream end of the center body44 and that fluidly connects to the upstream ends of the plurality ofpremix passages 61. The fuel pipe 45 actively injects fuel into thepremix passages 61 immediately downstream of the fill openings 61 a ofthe premix passages 61 in order to promote maximum mixing of the fueland air that travels downstream within the premix passages 61. Thus, asfar as the supply of air and fuel to the premix pilot nozzle 60 isconcerned, the embodiment depicted in FIGS. 10 and 12 can be deemed anembodiment that employs a passive air supply and an active fuel supply.

As schematically shown in FIG. 12, the angle of each angled premixpassage 61 is so configured so as to direct the fuel-air mix that isdischarged from the exit opening 61 b of each angled premix passage 61radially inwardly in a direction that crosses the axial path of the airthat exits from within the axially extending inner channel 53 of thepremix pilot nozzle 60 after having passed through the hollow interior51 of the center body 44 and imparts additional swirl to the flow offuel and air. The magnitude of the acute angle desirably measures on theorder of 4.5 degrees and can range from 3 degrees to 6 degrees.Moreover, due to the acute angle, the length of the mixing path withineach angled premix passage 61 of the embodiment of the premix pilotnozzle 60 depicted in FIG. 12 desirably is lengthened relative to thelength of the mixing path within each strictly axial premix passage 61that elongates strictly parallel to the symmetrically central axis 33 ofthe center body 44 and the premix pilot nozzle 60 in the FIG. 12embodiment.

FIG. 13 schematically illustrates still a further exemplary embodimentof the premix pilot nozzle 60 in a cross sectional view similar to theview shown in FIG. 3. In FIG. 13, the elements in common with theembodiments shown in FIGS. 3-5 are enumerated with the same designatingnumerals as found in FIGS. 3-5. In the embodiment schematically shown inFIG. 13, a passive supply of fuel and a passive supply of air are fed tothe premix passages 61 of the premix pilot nozzle 60. The embodiment ofFIG. 13 provides the premix pilot nozzle 60 in a configuration in whichthe premix passages 61 are arranged circumferentially around thedownstream end of the center body 44. Internally of the center body 44,the embodiment of FIG. 13 includes an air plenum 56 fluidly connectingto the fill openings 61 a of the premix passages 61. A passive flow ofair is carried from the head end volume 13 (FIG. 2) and supplied to theair plenum 56 via a plurality of radial air supply tubes 57 that extendthrough the axially elongating peripheral wall 38. The fuel supply forthe fuel outlet openings 49 in the swirler vanes 47 is tapped so thatsome of this fuel supply is diverted from the fuel outlet openings 49and provides a passive supply of fuel 31 that is carried via axiallyextending fuel conduits 55 downstream to the air plenum 56. Asschematically indicated in FIG. 13, each of the distal ends of theaxially extending fuel conduits 55 extends into the radial air supplytubes 57 near where the radial air supply tubes 57 connect to the airplenum 56. With this configuration, the fuel 31 is passively injectedinto the air flow 30 supplied via the radial air supply tubes 57 beforethat air flow 30 reaches the air plenum 56 and the fill openings 61 a ofthe premix passages 61. As in the other embodiments of the premix pilotnozzle 60, the fuel 31 and air 30 mixes while traveling downstreamwithin the premix passages 61. The fuel-air mix that leaves the exitopening 61 b of each premix passage 61 is thoroughly mixed and thuscombusts more efficiently to provide a small, well anchored premixedflame near the base of the fuel nozzle 12, thus anchoring the swirlingfuel air mixture exiting the fuel nozzle 12.

FIG. 14 schematically illustrates still a further exemplary embodimentof the premix pilot nozzle 60, in a cross sectional view similar to theview shown in FIG. 12. However, while the FIG. 14 embodiment has anactive fuel supply to the premix pilot nozzle 60 as in the FIG. 12embodiment, the FIG. 14 embodiment also has an active air supply to thepremix pilot nozzle 60. In FIG. 14, the elements in common with theembodiments shown in FIGS. 3-5, 12 and 13 are enumerated with the samedesignating numerals as found in FIGS. 3-5, 12 and 13. As schematicallyshown in FIG. 14, fuel from the annular fuel passage 46 is activelycontrolled to flow into the fuel premix injection ring 48 and exits outof the fuel outlet openings 49 defined through the swirler vanes 47. Thefuel ejected from the fuel outlet openings 49 is supplied into theradially outer air passage 50 for premixing fuel and air in the radiallyouter air passage 50 upstream of the combustion chamber reaction zone32. As air is directed against the air swirler vanes 47, a swirlingpattern is imparted to the air, and this swirling pattern facilitatesthe mixing of the air with the primary fuel that is ejected from thefuel outlet openings 49 of the air swirler vanes 47 into the passing airflow. The air/fuel mixture exiting the radially outer air passage 50flows into the combustion chamber reaction zone 32, where it iscombusted.

However, the embodiment of FIG. 14 provides the premix pilot nozzle 60in a configuration that is disposed circumferentially around thedownstream end of the center body 44. An actively controlled supply ofair 30 is provided to the premix passages 61 of the premix pilot nozzle60 via the hollow interior 51 defined by the inner cylindrical wall 54of the center body 44. In the exemplary embodiment shown in FIG. 14, anactively controlled supply of fuel is provided from the center body 44to the premix pilot nozzle 60. As schematically shown in FIG. 14, theportion of the fuel supply passage defined within the fuel pipe 45 has adownstream end that is disposed at the downstream end of the center body44 and that fluidly connects to the upstream ends of the plurality ofpremix passages 61. The fuel pipe 45 actively injects fuel 31 into thepremix passages 61 immediately downstream of the fill openings 61 a ofthe premix passages 61 in order to promote maximum mixing of the fueland air that travels downstream within the premix passages 61. In thismanner, the air flow 30 entering the fill opening 61 a of each premixpassage 61 in the premix pilot nozzle 60 entrains and mixes with thefuel 31 injected into each premix passage 61 and undergoes continuedmixing of the fuel-air mix while the fuel-air mix travels downstreamwithin the premix passages 61.

FIG. 15 schematically illustrates still a further exemplary embodimentof the premix pilot nozzle 60, in a cross sectional view. However, theFIG. 15 embodiment illustrates a breech-loaded premix pilot cylinder 35having at the downstream end thereof a premix pilot nozzle 60. In FIG.15, the elements in common with the embodiments shown in FIGS. 2-5 and11-13 are enumerated with the same designating numerals as found inFIGS. 2-5 and 11-13. As schematically shown in FIG. 15, air flow 30 fromthe head end volume 13 (FIG. 2) is actively controlled to flow past thefuel premix injection ring 48 and its swirler vanes 47. As schematicallyshown in FIG. 15, an actively controlled flow of fuel 31 is suppliedthrough the end plate 27 into the annular fuel passage 46 and thenceinto the fuel premix injection ring 48 and exits out of the fuel outletopenings 49 defined through the swirler vanes 47. The fuel ejected fromthe fuel outlet openings 49 is supplied into the radially outer airpassage 50 for premixing fuel and air in the radially outer air passage50 upstream of the combustion chamber reaction zone 32. As the air flow30 is directed against the air swirler vanes 47, a swirling pattern isimparted to the air, and this swirling pattern facilitates the mixing ofthe air with the primary fuel that is ejected from the fuel outletopenings 49 of the air swirler vanes 47 into the passing air flow. Theair/fuel mixture exiting the radially outer air passage 50 flows intothe combustion chamber reaction zone 32, where it is combusted.

As schematically shown in FIG. 15, the breech-loaded oil cartridge 37(which optionally can employ a gaseous fuel instead of liquid oil) andits surrounding breech-loaded premix pilot cylinder 35 slide into thehollow interior 51 defined by the inner cylindrical wall 54 of thecenter body 44, and the premix pilot flange 29 is connected to an endplate 27 of the combustor 16 by a seal 21 between the premix pilotflange 29 and the end plate 27. The cylindrical fuel cartridge 36defines a central fuel passage 37 through which an actively controlledsupply of fuel flows in the downstream direction as schematicallyindicated by the numeral 31. As schematically shown in FIG. 15, anactively controlled air flow 30 is provided through the premix pilotflange 27 and flows downstream in the annular channel formed between theexterior surface of the cylindrical fuel cartridge 36 and the interiorsurface of the breech-loaded premix pilot cylinder 35. As schematicallyshown in FIG. 15, premix pilot fuel 31 is actively controlled to flowinto the fuel pipe 45 that is connected to the upstream end of the fuelpremix pilot nozzle 60. As schematically shown in cross section in FIG.15, the fuel 31 from the fuel pipe 45 enters each premix passage 61 viaa fuel inlet 62 that is defined in the radially inwardly disposed wallthat defines each premix passage 61 so as to inject fuel into eachpremix passage 61 immediately downstream of the fill opening 61 a ofthat premix passage 61 in order to promote maximum mixing of the fueland air that travels downstream within the premix passages 61. In thismanner, the air flow 30 entering the fill opening 61 a of each premixpassage 61 in the premix pilot nozzle 60 entrains and mixes with thefuel 31 injected into each premix passage 61 and undergoes continuedmixing of the fuel-air mix while the fuel-air mix travels downstreamwithin the premix passages 61.

In each embodiment of the premix pilot 60 disclosed herein, the fuel-airmix that leaves the exit opening 61 b of each premix passage 61 isthoroughly mixed and thus combusts more efficiently to provide a small,well anchored premixed flame near the base of the fuel nozzle 12, thusanchoring the swirling fuel air mixture exiting the fuel nozzle 12. Theimproved flame stability enables lower fuel/air operations, thusextending LBO and the operating window of the gas turbine system 10below 3 ppm NOx emissions. The adaptability to both passive air andpassive fuel feeds enables a very simple lower cost design.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other and examples areintended to be within the scope of the claims if they include structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal languages of the claims.

What is claimed is:
 1. A fuel injector for a gas turbine engine,comprising: a. an axially elongating peripheral wall defining an outerenvelope of the injector, the wall having an interior surface definingan axially elongating interior cavity; b. a center body disposed withinthe axially elongating interior cavity, the center body defined by anexterior wall and an inner cylindrical wall, wherein the exterior wallincludes an upstream end and a downstream end of the center body, saiddownstream end disposed axially opposite the upstream end, the exteriorwall concentrically arranged about a longitudinal axis of the axiallyelongating peripheral wall, and wherein the inner cylindrical wall isconcentrically arranged about the longitudinal axis, and wherein theexterior wall and inner cylindrical wall define a hollow axiallyelongating interior passage radially therebetween through which airflows from the upstream end to the downstream end, and wherein thecenter body and the axially elongating peripheral wall define a primaryair flow channel therebetween; c. a fuel pipe positioned within thecenter body, wherein the fuel pipe extends axially from the upstream endto the downstream end of the center body, the fuel pipe defining a fuelpassage disposed radially outward from the longitudinal axis of theaxially elongating peripheral wall, the fuel pipe configured in fluidconnection to a source of fuel; d. a radial air supply tube, the radialair supply tube defining an auxiliary air passage through which air froma head end volume enters the axially elongating interior passage; and e.a premix pilot nozzle positioned at the downstream end of the centerbody, the premix pilot nozzle defining a plurality of axially extendingpremix passages in fluid communication with the fuel passage anddefining a plurality of exit openings at a downstream end of the premixpilot nozzle, the premix pilot nozzle defining at least one fill openingat an upstream end of the premix pilot nozzle, the at least one fillopening communicating a fluid from the interior passage to the pluralityof premix passages, the premix pilot nozzle defining an outlet at thedownstream end of the premix pilot nozzle, and wherein the premix pilotnozzle defines an axially extending inner channel radially inward of thefuel pipe extending upstream from the outlet to a downstream end of theinterior passage.
 2. The fuel injector of claim 1, further comprising: afuel cartridge disposed in the axially elongating interior cavity andthe axially extending inner channel, wherein the fuel cartridge definesa central fuel passage through which a supply of fuel flows in adownstream direction.
 3. The fuel injector of claim 1, wherein eachpremix passage of the premix pilot nozzle defines a fill opening of theat least one fill opening that admits fluid to flow into the respectivepremix passage and communicates fluidly with the interior passage of thecenter body.
 4. The fuel injector of claim 1, wherein the premixpassages are disposed between the inner cylindrical wall and theexterior wall.
 5. The fuel injector of claim 1, wherein the exit openingof each premix passage is arranged circumferentially around the innerchannel.
 6. The fuel injector of claim 1, wherein each premix passage isarranged circumferentially around the inner channel.
 7. The fuelinjector of claim 1, further comprising a plurality of radial air supplytubes, each radial air supply tube extending through the axiallyelongating peripheral wall and fluidly connecting with at least one ofthe at least one fill opening.
 8. The fuel injector of claim 1, whereinan actively controlled supply of air and/or fuel is configured to flowin the downstream direction of the interior passage defined by the innercylindrical wall.
 9. The fuel injector of claim 1, wherein the centerbody has a centrally symmetric axial centerline and each premix passagehas a premix axis about which its defining walls are concentricallydefined, and at least one of the premix passages is an angled premixpassage such that the premix axis of the at least one angled premixpassage is disposed at an acute angle with respect to the centrallysymmetric axial centerline of the center body.
 10. The fuel injector ofclaim 9, wherein the acute angle of each angled premix passage isconfigured and disposed so as to impart to the flow direction of afuel-air mix that discharges from the exit opening of each angled premixpassage a radially inwardly directed component in a direction that movestoward the centrally symmetric axial centerline of the center body.